Device for, and a method of, transcutaneous pressure waveform sensing of an artery and a related target apparatus

ABSTRACT

A device ( 20 ) for transcutaneous pressure waveform sensing of an artery. The device ( 20 ) having, in use, an application direction ( 43 ) towards the skin ( 46 ) of a user. The device ( 20 ) includes a pressure sensing head ( 37 ) having a distal end ( 36 ) and at least one skin depressing means ( 38 ) extending at least partially around the head ( 37 ) and having a distal surface ( 40 ). The pressure sensing head distal end ( 36 ) and skin depressing means distal surface(s) ( 40 ) are sized such that the pressure sensing head distal end ( 36 ) is spaced apart, in the application direction, from the skin depressing means distal surface(s) ( 40 ). A method of transcutaneous pressure waveform sensing and a target apparatus ( 100 ) are also disclosed.

FIELD OF THE INVENTION

The present invention relates to a device for, and a method oftranscutaneous pressure waveform sensing of an artery and a relatedtarget apparatus. Transcutaneous pressure waveform sensing is alsosometimes referred to as arterial tonometry or transcutaneous bloodpressure pulse waveform sensing.

BACKGROUND OF THE INVENTION

Transcutaneous pressure waveform sensing involves applying a tonometer(ie. a pressure sensor) to the skin of a patient over a superficialartery, such as the radial artery. The tonometer is applied with enoughdownward force to applanate (ie. partially flatten) the underlyingartery. When applanated, the pressure pulses are no longer taken upcircumferentially in the artery wall, but instead are transferredthrough the artery wall and surrounding tissue in a radial direction ofthe applanating force to the interface between the skin and the smallarea of the tonometer above the artery at which point the intra-arterialpressure waveform can now be faithfully recorded. The varying pulsatingforce applied to the tonometer by the transmitted intra-arterialpressure pulse waveform is continuously converted into an electricalsignal by a pressure transducer and plotted on a screen display whichallows a clinician to examine the intra-arterial pressure waveform ofthe patient. Analysing the pressure pulse waveform using knownappropriate software can provide diagnostic information to clinicians inrelation to areas such as: stiffness of arteries; susceptibility tomyocardial ischaemia; risk stratification of marginal hypertensives; andcardiovascular risk of type II diabetic patients.

The Colin Medical CBM-7000 is a known transcutaneous pressure sensingdevice that consists of a pressure pulse waveform detecting apparatuswhich is strapped around the wrist, a sphygmomanometer cuff which iswrapped around the arm, and a screen display. The pressure pulse wavedetecting apparatus has a chamber housing a semiconductor pressuresensor array. The pressure sensor array is positioned above the radialartery, and using hydraulic pressure, is pushed downwards to suitablyflatten the artery. The amount of pressure applied to the sensor arrayis dependent on the output signal recorded by these sensors. A centralprocessing unit (CPU) examines the output signals and gives a signal toa pressure valve to either reduce or increase the downward pressure onthe pressure sensor array. In other words, the CPU chooses the correctamount of tonometer downward pressure needed to applanate the arterysufficiently to obtain a strong arterial pressure waveform signal. Asimilar technique is used to correctly position the transducers justabove the radial artery. More particularly, if a strong pressurewaveform signal does not appear on any of the array of sensors, aservomotor will move the sensor array laterally until one of the sensorshas a suitably strong signal, again with the CPU comparing all outputsignals from the transducers. This is a time consuming process. At theend of this operation, the output signal will resemble the intraarterial blood pressure waveform, but in an analogue voltage signalform. A sphygmomanometer cuff is then used to determine brachial arterymaximum (“systolic”) and minimum (“diastolic”) pressures and thetransducer pulse waveform recorded by the radial artery tonometer iscalibrated according to these maximum/minimum values. The output monitorthen displays a continuous and calibrated radial blood pressurewaveforms. A disadvantage of this device is that it is complicated andtime consuming to set up for a measurement. Another disadvantage is thatthe device is expensive initially, and has high in-service costs due tothe electromechanical complexity of the pressure sensor module that isattached to the wrist.

The Millar Instruments SPT-301B Tonometer is another knowntranscutaneous pressure sensing device that is a hand-held pen-likedevice that contains a strain gauge on the end that converts amechanical force into an electrical signal. For the tonometer to sensethe arterial pressure, a downward force on the tonometer over theunderlying artery is manually applied by the user to applanate theartery. With this downward pressure, the pressure transducer on the endof the tonometer in contact with the skin will begin to sense thechanging force resulting from the intra-arterial blood pressurepulsations. This tonometer is presently internationally accepted as themost accurate sensor for making transcutaneous arterial pressurewaveform recordings. The size of the pressure sensing transducer in theMillar tonometer is very small and as a result it has the disadvantagethat it has to be precisely positioned above the radial artery toachieve accurate results, which is difficult. Another disadvantage ofthe Miller tonometer is that, because it is pencil-shaped, it flattensonly a small area when the sensing end is pushed over the artery, andthis can lead to the artery moving laterally out from under the sensorinto the uncompressed area and so giving no arterial pressure waveformsignal in the sensor.

The Hypertension Diagnostics Inc CD-2000 is another known transcutaneousarterial pressure sensing device that includes a fixed pressure sensorthat is strapped over the radial artery. The operator rotates ascrew-threaded wheel to push the pressure sensor down over the arteryand applanate the artery until a strong arterial pressure is recorded.The head of the device in contact with the skin is 1˜1.5 cms indiameter. Disadvantages of the CD-2000 device are it is complicated andtime consuming to set up for a measurement and it is expensive. Further,it has not been shown that this tonometer is able to faithfullyreproduce the intra-arterial waveform.

It is an object of the present invention to substantially overcome or atleast ameliorate one or more of the deficiencies of the prior artdevices discussed above.

SUMMARY OF THE INVENTION

Accordingly, in a first aspect, the present invention provides a devicefor transcutaneous pressure waveform sensing of an artery, the devicehaving, in use, an application direction towards the skin of a user inthe direction of an underlying artery and including:

-   -   a pressure sensing head having a distal end; and    -   at least one skin depressing means substantially adjacent the        pressure sensing head and having a distal surface, wherein the        pressure sensing head distal end and skin depressing means        distal surface(s) are sized such that the pressure sensing head        distal end is spaced apart, in the application direction, from        the skin depressing means distal surface(s).

In one form, the pressure sensing head distal end protrudes from theskin depressing means distal surface(s) in the application direction.

In another form, the skin depressing means distal surface(s) protrudesfrom the pressure sensing head distal end in the application direction.

In an embodiment, the distance between the skin depressing means distalsurface and the pressure sensing head distal end is fixed. The distancebetween the skin depressing means distal surface(s) and the pressuresensing head distal end is preferably approximately 1.5 mm to 2.0 mm,for the radial artery.

In another embodiment, the distance between the skin depressing meansdistal surface(s) and the pressure sensing head distal end is variable.The device preferably includes a handle and the distance between theskin depressing means distal surface(s) and the handle varies relativeto the application pressure applied to the user's skin and the distancebetween the pressure sensing head distal end and the handle is fixed. Inthis form, the skin depressing means is/are preferably formed from acompressible material. Alternatively, the device includes a handle andthe distance between the pressure sensing head distal end and the handlevaries relative to the application pressure applied to the user's skinand distance between the skin depressing means distal surface(s) and thehandle is fixed. In this form, the device preferably includes acompression spring arrangement between the pressure sensing head and thehandle.

In one arrangement, the device preferably has a single skin depressingmeans. In this arrangement, the skin depressing means has asubstantially annular distal surface.

In another arrangement, the device has a single skin depressing meanspositioned, in use, on one side of the artery.

In a further arrangement, the device has a pair skin depressing meanspositioned, in use, either side of the artery. In a preferred from ofthis arrangement, the skin depressing means distal surface(s) are eachhemispherical. In another form of this arrangement, the skin depressingmeans distal surface(s) are each oriented substantially normally to thelongitudinal direction of the artery.

In a second aspect, the present invention provides a method oftranscutaneous pressure waveform sensing of an artery, the methodincluding the steps of:

-   -   flattening and depressing at least some of the skin around the        artery and displacing same, in an application direction towards        the artery, to a first depth; and    -   flattening and depressing the skin over the artery and        displacing same, in the application direction, to a second depth        that differs than the first depth.

In one form, the first depth is greater than the second depth.

In another form, the second depth is greater than the first depth.

In one embodiment, the distance between the first depth and the seconddepth is fixed. The distance between the first depth and the seconddepth is preferably approximately 1.5 mm to 2.0 mm.

In another embodiment, the distance between the first depth and thesecond depth is variable.

In one arrangement, the method includes flattening, depressing anddisplacing a circular region of the skin over the artery. In thisarrangement, the method also preferably includes flattening, depressingand displacing an annular region of the skin around the artery.

In another arrangement, the method includes flattening, depressing anddisplacing the skin around the artery on one side of the artery.

In a further arrangement, the method includes flattening, depressing anddisplacing the skin around the artery on both sides of the artery. In apreferred form of this arrangement, the method preferably includesflattening, depressing and displacing a pair of hemispherical regions ofthe skin around the artery, the regions being either side of the artery.In another form of this arrangement, the method preferably includesflattening, depressing and displacing a pair of regions of the skinaround the artery, the regions being either side of the artery andoriented substantially normally to the longitudinal direction of theartery.

In a third aspect, the present invention provides a target apparatus foruse with a device for transcutaneous waveform pressure sensing of anartery, the device having an end pressure sensing head protrudingtherefrom, the apparatus including:

-   -   an skin adhesive pad;    -   a target marking on the pad; and    -   skin compression means at least partially around the target        marking,    -   wherein, during use, the device is applied to the pad with the        device pressure sensing head over the target marking and the        device end over the skin compression means whereby, when the        device is depressed into the skin during use, the skin beneath        the target marking and the skin compression means are displaced        to differing depths.

The target marking is preferably substantially circular.

The skin compression means are preferably a pair of substantiallyrectangular pads either side of the target marking.

In a fourth aspect, the present invention provides a device fortranscutaneous pressure waveform sensing, the device including:

-   -   a pressure sensing head having a distal end; and    -   a collar extending at least partially around the head and having        a distal surface, wherein the pressure sensing head distal end        and collar are sized such that the pressure sensing head        protrudes from the collar distal surface.

In use, when applied to a patient's skin over an underlying artery, atleast some of the skin around the artery is flattened and depressed bythe collar to a first depth and the skin over the artery is flattenedand depressed by the pressure sensing head distal end to a second depthgreater than the first depth.

In a fifth aspect, the present invention provides a method oftranscutaneous pressure waveform sensing, the method including the stepsof:

-   -   flattening and depressing at least some of the skin around an        underlying artery and displacing same to a first depth; and    -   flattening and depressing the skin over the underlying artery        and displacing same to a second depth greater than the first        depth.

The skin around the artery is preferably compressed by the collar eitherside of the longitudinal direction of the artery (ie. the lateralsides). The width of the skin area flattened (and thus the width of thecollar) either side of the artery, in a direction normal to thelongitudinal direction of the artery, is dependent upon the differentphysiology surrounding the specific artery (eg, radial, carotid,femoral). For the radial artery, it is desirable to compress about 3times the unflattened width of the artery in each direction lateral tothe direction of the artery.

For the radial artery the difference between the first and second depthis preferably approximately 1.5-2.0 mm.

For use with the radial artery, the collar is configured to besymmetrical in relation to the longitudinal direction of the artery andnon-symmetrical in relation to a direction normal to the longitudinaldirection of the artery, with the length of the collar from the pressuresensing head towards the patient's wrist being smaller than the lengthof the collar from the pressure sensing head towards the patient'selbow.

For use with the carotid artery, the collar is configured to benon-symmetrical in relation to the longitudinal direction of the arteryand non-symmetrical in relation to a direction normal to thelongitudinal direction of the artery, with the length of the collar fromthe pressure sensing head towards the front of the patient's throatbeing smaller than the length of the collar from the pressure sensinghead towards the patient's neck and the length of the collar from thepressure sensing head towards the patient's shoulder being smaller thanthe length of the collar from the pressure sensing head towards thepatient's head.

The article entitled “Arterial Tonometry: Review and Analysis” by GaryM. et al (J. Biomechanics Vol. 16. No. 2. pp. 141-152, 1983) sets outthe optimal width of the pressure sensing head relative to uncompressedartery diameter. The preferred diameter of the pressure sensing head isless than or equal to the width of the flattened section of theunderlying artery. However, for maximum flexibility in positioning thesensor, it is desirable to have the pressure sensing head as wide aspossible (witness the limitations of the Millar sensor).

In one preferred form for the radial artery, the pressure sensing headis circular in cross section and the collar is annular in cross section,and the diameter of the pressure sensing head is approximately 3.5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional side view of a first embodiment of a devicefor transcutaneous pressure waveform sensing according to the invention;

FIG. 2 is a top view of a collar used with the device shown in FIG. 1;

FIG. 3 is a bottom view of the collar shown FIG. 2;

FIG. 4 is a side view of the collar shown in FIG. 2;

FIG. 5 is a cross-sectional side view of the collar shown in FIG. 2;

FIG. 6 is a cross-sectional side view of the device shown in FIG. 1without the collar;

FIG. 7 is a front view of the device shown in FIG. 6;

FIG. 8 is a top view of the device shown in FIG. 6;

FIG. 9 is a side view of the device shown in FIG. 6;

FIG. 10 is a bottom view of the device shown in FIG. 6;

FIG. 11 is a side view of the device shown in FIG. 1 over a patient'sskin, prior to use;

FIG. 12 is a side view of the device shown in FIG. 1, during use.

FIG. 13 is an inverted side view of a second embodiment of a device fora transcutaneous pressure waveform sensing according to the invention;

FIG. 14 is a bottom view of the device shown in FIG. 13;

FIG. 15 is an inverted front view of the device shown in FIG. 13;

FIG. 16 is an inverted side view of a third embodiment of a device fortranscutaneous pressure waveform sensing according to the invention;

FIG. 17 is a bottom view of the device shown in FIG. 16;

FIG. 18 is an inverted front view of the device shown in FIG. 16;

FIG. 19 is an exaggerated cross sectional side view of the device shownin FIG. 16 during use;

FIG. 20 is an inverted side view of a fourth embodiment of a device fora transcutaneous pressure waveform sensing according to the invention;

FIG. 21 is a bottom view of the device shown in FIG. 20;

FIG. 22 is an inverted front view of the device shown in FIG. 20;

FIG. 23 is a side view of a first embodiment of a target apparatusaccording to the invention;

FIG. 24 is a top view of the apparatus shown in FIG. 23; and

FIG. 25 is a side view of the apparatus shown in FIG. 23 with anadjacent transcutaneous waveform pressure sensing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the FIGS. 1 to 12, there is shown a device 20 fortranscutaneous pressure waveform sensing according to a first embodimentof the invention. The device 20 is comprised of a housing 21 formed froma base 22 and top 24, which are both formed from poly vinyl chloride(PVC).

An internal chassis 26 within the base 22 supports a pressure transducer28, in the form of a Pressure Sensor model No. MPX2300DT1, produced bythe Motorola Company. The chassis 26 also includes an opening 30 whichallows the sensor 28 to communicate pressure changes brought about in apocket of gel 32, preferably dielectric silicone gel—grade 537 producedby the Dow Corning Company. The gel 32 is retained in the chassis 26 bya silicone boot 34, preferably of shore hardness 55.

The exterior surface of the boot 34 that is denoted 36 represents thedistal end of an overall “pressure sensing head” 37 formed by components28, 30, 32 and 34.

The device 20 also include a “skin depression means” in the form of anannular PVC collar 38 around the head 37. The collar 38 has a distalsurface denoted 40, an external diameter of 13.6 mm and a thickness inthe direction of axis 40 of 2.5 mm. The internal diameter of the collar38 is approximately 6 mm and is a snug fit around the cylindrical sidewall of the boot 34. The collar 38 is an interference locating fit overthe boot 34.

It is important to note that the distal end 36 of the pressure sensinghead 37 protrudes in the direction of axis 42 from the distal surface 40of the collar 38. It is also important to note that the axis issubstantially parallel to what is termed the “application direction”,being the general direction (as represented by arrow 43) the device 20is applied, in use, towards the skin and the underlying artery.

As best shown in FIG. 8, the device 20 also include an electricalconnection 44 which allow electrical signals generated by the HVPS 28 tobe communicated to appropriate computer equipment and processingsoftware, as is well known in the art and which will not be describedfurther.

The operation of the device 20 will now be described with particularreference to FIGS. 11 and 12. FIG. 11 shows the device 20 positionedover the skin 46 above the radial artery 48 of a human. FIG. 12 showsthe device 20 after depression into the skin 46 in the applicationdirection to cause flattening of the artery 48. As the distal end 36 ofthe pressure sensing head 37 protrudes from the distal surface 40 of thecollar 38. This results in the skin 46 a adjacent the pressure sensinghead 37 being displaced about 2 mm more than the skin 46 b adjacent thecollar 38, which stretches the tissue beneath the skin 46 b (ie. thetissue beneath the collar 38).

The correct amount of depression of the device 20 into the skin 46 isdetermined by the clinician manipulating the device 20 whilst watching agraphical representation of the intra-arterial pressure profile of thepatient on a display screen (not shown). If the device 20 has not beendepressed into the skin 46 far enough, a low amplitude and noisy pulsewaveform signal will be evident. If the device 20 has been depressed toofar into the skin 46 any pulse waveform signal will be lost due to theartery 46 being excessively flattened into occlusion. The clinician candetermine when the device 20 has been optimally depressed into the skin46 when a large amplitude pulse waveform signal is evident on thedisplay screen.

The clinician can also choose collars of different thicknesses to adjustthe relative amounts of depression, depending on the type and locationof artery and the physical characteristics of the patient (eg. age,muscle tone).

The device 20 provides a superior quality signal than prior art devicesbecause it compresses the soft tissue on either side of the artery 48which prevents the artery 48 from moving laterally away from the distalend 36 of pressure sensing head during applanation.

Referring to FIGS. 13 to 15 there is shown a device 60 fortranscutaneous pressure waveform sensing according to a secondembodiment of the invention. The device is similar to the firstembodiment shown in FIGS. 1 to 12 and like reference numerals will beused to indicate like features. The main difference between the devices20 and 60 is that the device 60 has a pair of skin depression means inthe form of solid foam pads 62 a and 62 b. During use, the device 60 isoriented such that the pads 62 a and 62 b lie either side of the arterybeing measured. Similar to the first embodiment, the device 60 providesa superior quality signal than prior art devices because it compressesthe soft tissue on either side of the artery, which thereby prevents theartery from moving laterally away from the distal end 36 of the pressuresensing head 37 during applanation.

Similar to the first embodiment, the clinician can also choose pads ofdifferent thicknesses to adjust the relative amounts of depression.

Referring to FIGS. 16 to 19 there is shown device 70 for transcutaneouspressure waveform sensing according to a third embodiment of theinvention. The device 70 is similar to the device 60 and like referencenumerals will be used to denote like features. The main differencebetween the devices 60 and 70 is that, in the device 70, the distalsurfaces 40 of the two pads 62 a and 62 b are displaced further awayfrom the housing 21 of the device 70 than the distal end 36 of thepressure sensing head 37.

During use, the device 70 depresses and displaces the skin 46 a abovethe artery 48 and the skin 46 b either side of the artery 48 in themanner indicated by the (exaggerated) representation shown in FIG. 19.In addition to the advantages provided by the earlier embodiments, thedevice 70 finds particular application in sensing an artery 48 betweentendons or ligaments 74 as the pads 62 a and 62 b result in additionaldownwards displacement of such tendons or ligaments to allow betteraccess to the artery 48 for applanation.

Referring to FIGS. 20 to 22 there is shown a device 80 fortranscutaneous pressure waveform sensing according to a fourthembodiment of the invention. The device 80 is similar to the device 70and like reference numerals will be used to denote like features. Themain difference between the device 80 and 70 is that the pads 62 a and62 b in the device 80 are formed from hollow foam which are compressiblein response to the pressure applied in the application direction towardsthe skin 46. This allows the clinician to vary the amount of relativedisplacement between the region of skin 46 a above the artery 48 and theregions of skin 46 b either side of the artery 48.

FIGS. 23 to 25 show a target apparatus 100 according to a firstembodiment of the invention. The apparatus 100 is used with a device 102for transcutaneous waveform pressure sensing. The device 102 is similarto the devices 60, 70 and 80 accept it does not have the pads 62 a and62 b and instead only has the pressure sensing head 37 solely protrudingfrom the housing 21. The target apparatus 100 has a skin adhesive pad104 a target marking 106 on the pad 104 and skin depression means, inthe form of foam pads 108 a and 108 b.

In use, the target apparatus 100 is applied to the skin centered abovethe artery to be measured and with the pads 108 a and 108 b orientedeither side of the artery. The target marking 106 represents where thepressure sensing head 37 of the device 100 should be positioned duringuse. When the pressure sensing device 102 is depressed into the skin ofthe user above the target apparatus 100, the skin 46 a beneath thetarget marking (and thus beneath the pressure sensing head 37) isdisplaced to a different depth to the skin beneath the pads 108 a and108 b. This results in the skin being displaced in a similar manner tothat is shown in FIG. 12.

The preferred embodiments of devices and methods of use according to theinvention are easier to operate and provide superior quality signalsthan prior art devices/methods. Generally speaking, this is because they‘condition’ the skin and underlying physiology surrounding the artery inorder to better locate and sense the pressure waveform in the underlyingartery of interest. They also allow the use of an optimally-sizedpressure sensing head, which is able to pick up an accurate signal fromthe applanated artery, that, due to the skin depressing means, does notneed to be as accurately positioned to the centre of the underlyingartery as prior art devices (eg, the Millar tonometer). The latter isfirstly because the reduced depression of the skin at least on the(lateral) sides of the artery assists in maintaining the preferredsymmetrical position between the pressure sensing head and the artery byreducing movement of the artery laterally away from the pressure sensinghead during applanation. Such movement is a particular problem whenattempting to monitor the pressure of an artery with nearby collateralanatomy such as tendons and muscle etc. The partial depression of theskin lateral to the artery provides a stabilising pressure whichmaintains the artery in the optimal position relative to the pressuresensing head. Secondly, the width of the pressure sensing head isoptimal for the underlying artery according to the Drzewiecki research,which is not the case for the prior art devices.

The preferred size and shape of the pressure sensing head and collar,and the amount by which the distal end of the head protrudes, aredetermined by trial and error and are dependent on the type, size andlocation of the superficial artery which is to be measured, and theanatomy surrounding the artery.

Although the invention has been described with reference to a preferredembodiment, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms. For example:

-   -   (a) the sensor may be hand-held or be hands-free with some wrist        attachment mechanism;    -   (b) there may be some mechanical mechanism for applying the        downward applanation pressure;    -   (c) the sensor may have fixed or replaceable collars;    -   (d) different collars may be chosen for the same artery site        depending upon the depth of the artery below the skin in a        particular patient;    -   (e) there may be integrated into the sensor construction a        mechanism for moving an adjustable-depth collar up and down to        vary the height difference between the sensor and collar to an        optimal height during the study;    -   (f) the pressure sensing area may be other than circular; and    -   (g) the pressure sensor may operate in a sensing method other        than described here for example, pressure may be sensed across        the sensing area by piezoelectric sensor, by a strain-gauge        pressure sensors, by a fibre optic pressure sensors, etc.

1. A device for transcutaneous pressure waveform sensing of an artery,the device having, in use, an application direction towards the skin ofa user in the direction of an underlying artery and including: apressure sensing head having a distal end; and at least one skindepressing means substantially adjacent the pressure sensing head andhaving a distal surface, wherein the pressure sensing head distal endand skin depressing means distal surface(s) are sized such that thepressure sensing head distal end is spaced apart, in the applicationdirection, from the skin depressing means distal surface(s).
 2. Thedevice as claimed in claim 1, wherein the pressure sensing head distalend protrudes from the skin depressing means distal surface(s) in theapplication direction.
 3. The device as claimed in claim 1, wherein theskin depressing means distal surface(s) protrudes from the pressuresensing head distal end in the application direction.
 4. The device asclaimed in claim 1, wherein the distance between the skin depressingmeans distal surface and the pressure sensing head distal end is fixed.5. The device as claimed in claim 4, wherein distance between the skindepressing means distal surface(s) and the pressure sensing head distalend is approximately 1.5 mm to 2.0 mm.
 6. The device as claimed in claim1, wherein distance between the skin depressing means distal surface(s)and the pressure sensing head distal end is variable.
 7. The device asclaimed in claim 6, wherein the device includes a handle and thedistance between the skin depressing means distal surface(s) and thehandle varies relative to the application pressure applied to the user'sskin and the distance between the pressure sensing head distal end andthe handle is fixed.
 8. The device as claimed in claim 6, wherein theskin depressing means is/are formed from a compressible material.
 9. Thedevice as claimed in claim 6, wherein the device includes a handle andthe distance between the pressure sensing head distal end and the handlevaries relative to the application pressure applied to the user's skinand distance between the skin depressing means distal surface(s) and thehandle is fixed.
 10. The device as claimed in claim 9, wherein thedevice includes a compression spring arrangement between the pressuresensing head and the handle.
 11. The device as claimed in claim 1,wherein the device has a single skin depressing means.
 12. The device asclaimed in claim 11, wherein the skin depressing means has asubstantially annular distal surface.
 13. The device as claimed in claim1, wherein the device has a single skin depressing means positioned, inuse, on one side of the artery.
 14. The device as claimed in claim 1,wherein the device has a pair skin depressing means positioned, in use,either side of the artery.
 15. The device as claimed in claim 14,wherein the skin depressing means distal surface(s) are eachhemispherical.
 16. The device as claimed in claim 14, wherein the skindepressing means distal surface(s) are each oriented substantiallynormally to the longitudinal direction of the artery.
 17. A method oftranscutaneous pressure waveform sensing of an artery, the methodincluding the steps of: flattening and depressing at least some of theskin around the and displacing same, in an application direction towardsthe artery, to a first depth; and flattening and depressing the skinover the artery and displacing same, in the application direction, to asecond depth that differs than the first depth.
 18. The method asclaimed in claim 17, wherein the first depth is greater than the seconddepth.
 19. The method as claimed in claim 17, wherein the second depthis greater than the first depth.
 20. The method as claimed in claim 17,wherein the distance between the first depth and the second depth isfixed.
 21. The method as claimed in claim 21, wherein the distancebetween the first depth and the second depth is approximately 1.5 mm to2.0 mm.
 22. The method as claimed in claim 17, wherein the distancebetween the first depth and the second depth is variable.
 23. The methodas claimed in claim 17, including flattening, depressing and displacinga circular region of the skin over the artery.
 24. The method as claimedin claim 17, including flattening, depressing and displacing an annularregion of the skin around the artery.
 25. The method as claimed in claim17, including flattening, depressing and displacing the skin around theartery on one side of the artery.
 26. The method as claimed in claim 17,including flattening, depressing and displacing the skin around theartery on both sides of the artery.
 27. The method as in claimed claim26, including flattening, depressing and displacing a pair ofhemispherical regions of the skin around the artery, the regions beingeither side of the artery.
 28. The method as claimed in claim 26,including flattening, depressing and displacing a pair of regions of theskin around the artery, the regions being either side of the artery andoriented substantially normally to the longitudinal direction of theartery.
 29. A target apparatus for use with a device for transcutaneouswaveform pressure sensing of an artery, the device having an end with apressure sensing head protruding therefrom, the apparatus including: anskin adhesive pad; a target marking on the pad; and skin compressionmeans at least partially around the target marking, wherein, during use,the device is applied to the pad with the device pressure sensing headover the target marking and the device end over the skin compressionmeans whereby, when the device is depressed into the skin during use,the skin beneath the target marking and the skin compression means aredisplaced to differing depths.
 30. The apparatus of claim 29, whereinthe target marking is substantially circular.
 31. The apparatus of claim30, wherein the skin compression means are a pair of substantiallyrectangular pads either side of the target marking.